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Re: Flat plate punching shear

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Anantha Narayan,

1. Is there any rule of thumb to calculate/use for the bending stiffness factor for edge/corner columns, since you would expect them to crack and have a lesser resistance to rotation. I currently use 1.0 for all columns which is probably overconservative for edge columns.

You would have to calculate this for each situation. For the lower levels of a multi-story building the compression from the weight of the floors above will dominate the relatively small moments from the floor being designed and the columns will be in compression and uncracked. Therefore you would need to use the full column stiffness. For the upper floors where the tension may dominate you could do a reduction, but you would need to determine it for each column at each floor under vertical loading (ignoring wind and earthquake loading).

2. Currently I am using the moments from the program to design the studrails. The moments, I presume, is used by the program to come up with the flexural reinforcement for the slab. In that case, is there a reduced value of moment that can be used to design for shear since only a part of it will contribute to shear, or is it conservative to design for the entire moment?

The moment in the column must be transferred through the slab column connection. Some is transferred directly and some through torsion but it is all transferred through the punching shear perimeter. There is no reduction possible.

Anantha Narayan

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